lean-png

Use when fixing merge conflicts on agent PRs, rebasing stale branches, or deciding whether to salvage vs. redo a PR. Also use when a rebase/fix-PR plan issue is claimed.

Standard claim/branch/verify/publish workflow for pod agent sessions. Read this skill at the start of any feature, review, summarize, or meditate session.

Use when Lean 4 proofs involve ByteArray, Array, List indexing, getElem, length lemmas, take/drop, or roundtrip proofs over byte collections.

Use when proving that Lean 4 functions preserve existing bytes (prefix/content preservation), compose getElem_lt proofs through recursive structures, prove append-only buffer invariants, or characterize what new bytes a function produces (raw extract, RLE all-equal, element-wise correspondence).

Use when Lean 4 gives "motive is not type correct", max recursion on List.ofFn, rewriting fails due to dependent types, or cross-file visibility issues with private/protected.

Use when Lean 4 proofs involve fuel-based recursion, proving fuel independence, loop invariants, copyLoop-style patterns, suffix/append extension lemmas, or maxRecDepth/maxHeartbeats tuning.

Use when working on Lean 4 proofs involving Option or Except monad, do-notation unfolding, guard patterns, bind handling, join points, forIn loops in specifications, or Id monad loop invariants (Id.run do with for loops).

Use when a Lean 4 tactic fails or is unavailable — such as ring, set, push_neg, by_contra, field_simp, rcases, norm_num, or obtain — because this project does not use Mathlib.

Use when proving parsing completeness theorems — that a parsing function returns .ok when given well-formed input, or that spec-level success implies native success. Also use when proving position bounds, eliminator lemmas, or chaining monadic parsing steps in Except/Option.

Use when proving encode/decode roundtrip theorems, suffix invariance (_append lemmas), goR (decode-with-remaining) patterns, padding extraction, or composing per-level roundtrip proofs into a unified theorem.

Use when simp only fails unexpectedly in Lean 4, or when dealing with Bool vs Prop conditions, filter+lambda, let bindings in omega, linter false positives, or hypothesis normalization mismatches.

Use when Lean 4 proofs involve UInt8/UInt16/UInt32/BitVec conversions, bv_decide, or bridging between numeric types and Nat.

Use when Lean 4 proofs involve well-founded recursion, termination_by, f.induct functional induction, WF function unfolding, or converting fuel-based functions to WF recursion.

Use when implementing or proving properties about PNG chunk parsing, serialization, CRC32 validation, chunk sequence ordering, or IHDR/IEND structure.

Use when proving PNG scanline filter/unfilter roundtrip theorems, UInt8 modular arithmetic invertibility, Paeth predictor properties, or Average predictor floor-division patterns.

Use when implementing or proving properties about Adam7 interlacing, sub-image extraction, pixel scatter/gather, or interlace index bijectivity.

Use when reviewing Lean proof quality, cleaning up proofs after getting them to work, or performing a review session on a proof file. Also use when the review command targets a Lean file.

Use when converting `]!` runtime bounds checks to proven-bounds `]` access in Lean 4. Covers guard capture, omega proofs, caller propagation, loop bound capture, and common pitfalls.